This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-001451, filed Jan. 9, 2001; No. 2001-343575, filed Nov. 8, 2001; No. 2001-395846, filed Dec. 27, 2001; and No. 2001-395847, filed Dec. 27, 2001, the entire contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to a cathode-ray tube (CRT) apparatus, and more particularly to a cathode-ray tube apparatus with an electron gun assembly capable of effecting dynamic astigmatism compensation.
2. Description of the Related Art
In general, a color cathode-ray tube apparatus comprises an in-line electron gun assembly, which emits three electron beams, and a deflection yoke which produces deflection magnetic fields for deflecting the three electron beams emitted from the electron gun assembly. Specifically, the deflection yoke produces non-uniform magnetic fields comprising a pincushion-shaped horizontal deflection magnetic field 10, as shown in FIG. 9A, and a barrel-shaped vertical deflection magnetic field.
An electron beam 6, which has passed through the non-uniform magnetic fields, suffers a deflection aberration, i.e. an astigmatism due to the deflection magnetic fields. Specifically, the electron beam 6 traveling toward a peripheral portion of a phosphor screen receives a force 11V which causes the electron beam 6 to be vertically over-focused due to deflection aberration. As is shown in FIG. 9B, a beam spot on the peripheral portion of the phosphor screen is deformed to include a vertically spread blur 12 and a horizontally spread core 13. The deflection aberration suffered by the electron beam increases as the size of the tube increases and the deflection angle increases. The deformation of the beam spot will considerably degrade the resolution at the peripheral portion of the phosphor screen.
Jpn. Pat. Appln. KOKAI Publication No. 61-99249 discloses electron gun assemblies as means for improving the degradation in resolution due to deflection aberration. Each of these electron gun assemblies has a common basic structure, as shown in FIG. 10A, which comprises first to fifth grids. An electron beam generating section GE, a quadrupole lens QL and an ultimate main lens EL are formed in the direction of travel of electron beams. The quadrupole lens QL is formed by providing each of the opposing faces of adjacent electrodes with three non-axially symmetric electron beam passage holes (for example, three horizontally elongated electron beam passage holes are provided in one electrode and three vertically elongated electron beam passage holes are provided in the other electrode, as shown in FIGS. 10B and 10C).
In this electron gun assembly, the lens powers of the quadrupole lens QL and ultimate main lens EL are varied in synchronism with a variation of deflection magnetic fields. Thereby, the deflection aberration suffered by the electron beam deflected onto the peripheral portion of the phosphor screen is reduced, and the deformation of the beam spot is improved.
In this type of electron gun assembly, however, when an electron beam is deflected onto a peripheral portion on the phosphor screen, the effect of deflection aberration is very great. Thus, even if blur of the beam spot is eliminated, horizontal deformation cannot fully be corrected.
Jpn. Pat. Appln. KOKAI Publication No. 3-93135 discloses an electron gun assembly with a double-quadrupole lens structure as another means for improving the degradation in resolution due to deflection aberration. In this electron gun assembly, as shown in FIGS. 11A and 11B, two quadrupole lenses with different polarities are formed on the cathode side of a main lens. These two quadrupole lenses are operated in synchronism with deflection magnetic fields.
In this electron gun assembly, as shown in FIGS. 11A and 11B, the angle of incidence of an electron beam on the phosphor screen 3 is made substantially equal in horizontal and vertical directions when the electron beam is focused on a central portion of the phosphor screen (a non-deflection mode indicated by a solid line) and when the electron beam is deflected on a peripheral portion of the phosphor screen (a deflection mode indicated by a broken line). Thereby, a horizontal deformation of the beam spot on the peripheral portion of the phosphor screen is improved, as shown in FIG. 11C.
However, if the above-described double-quadrupole lens structure is employed, the front-side quadrupole lens situated on the cathode side vertically focuses the electron beam and horizontally diverges the electron beam, as this lens is operated by produced deflection magnetic fields. As a result, the horizontal dimension of the electron beam incident on the main lens increases.
Consequently, part of the electron beam passes through a region that is horizontally away from the center axis of the main lens, and is greatly affected by spherical aberration of the main lens. Specifically, the beam spot on the peripheral portion of the phosphor screen is shaped to have a horizontal halo portion.
In order to eliminate the effect of the horizontal spherical aberration of the main lens due to the front-stage quadrupole lens, it is necessary to limit the divergence angle of the electron beam to such a degree that the beam suffers no effect of lens aberration in accordance with the lens aperture of the main lens when the quadrupole lens is operated.
Assume that when the electron beam is to be focused on the peripheral portion of the phosphor screen, the horizontal divergence angle of the electron beam incident on the main lens is set at a just divergence angle at which the beam suffers no effect of an aberration component of the main lens. In this case, the front-stage quadrupole lens operates, by its inherent behavior, to increase the horizontal divergence angle of the electron beam when the beam is deflected from the center to the peripheral area of the phosphor screen. As a result, the horizontal divergence angle of the electron beam in the non-deflection mode becomes smaller than that in the deflection mode. Accordingly, the horizontal magnification of the total lens action of this electron gun in the non-deflection mode becomes greater than that in the deflection mode, and the horizontal dimension of the beam spot on the center area of the phosphor screen increases.
On the other hand, assume that when the electron beam is to be focused on the center portion of the phosphor screen, the horizontal divergence angle of the electron beam incident on the main lens is set at a just divergence angle at which the beam suffers no effect of an aberration component of the main lens. In this case, the horizontal divergence angle of the electron beam in the deflection mode gradually increases and gradually suffers the effect of the aberration component of the main lens. As a result, the beam spot on the peripheral portion of the phosphor screen is shaped to have a horizontal halo portion.
If the horizontal divergence angle is affected by the front-stage quadrupole lens, the horizontal dimension of the beam spot increases at either a peripheral portion or a central portion of the phosphor screen.
In addition, the structure wherein double-quadrupole lenses with different polarities are disposed on the cathode side of the main lens has a problem that a dynamic focus voltage is increased. If two quadrupole lenses with different polarities are created at the same time, the electron gun assembly operates as if a cylindrical lens were created between the two quadrupole lenses. As a result, an imaginary object point for the main lens is shifted backward from the main lens side to the cathode side.
Moreover, in this structure comprising the double-quadrupole lenses with different polarities, the two quadrupole lenses act so as to mutually cancel their lens powers. For this reason, the lens sensitivity of each quadrupole lens needs to be increased. For example, as shown in FIGS. 12A and 12B, the lens sensitivity can be increased by creating a quadrupole lens between electrodes each having upright projection portions extending in the direction of travel of the electron beam. However, with this electrode structure, a variance tends to occur in precision of positions of the upright projection portions and a stable operation is unexpectable.
As has been described above, with the cathode-ray tube apparatus having the conventional structure, the deformation of the beam spot on the peripheral portion of the phosphor screen is not fully corrected and good focus characteristics cannot be obtained over the entire phosphor screen.
The present invention has been made in consideration of the above problems and its object is to provide a cathode-ray tube apparatus capable of forming a beam spot with a good shape over the entire area of a phosphor screen.
According to a first aspect of the invention, there is provided a cathode-ray tube apparatus comprising: an electron gun assembly having an electron beam generating section which generates at least one electron beam, and a main electron lens section which focuses the electron beam emitted from the electron beam generating section on a phosphor screen; and a deflection yoke which produces deflection magnetic fields for deflecting the electron beam emitted from the electron gun assembly and causing the electron beam to horizontally and vertically scan the phosphor screen, wherein the electron gun assembly comprises a plurality of electrodes including a cathode supplied with a voltage of a relatively low first level, which constitute the electron beam generating section, at least one focus electrode supplied with a focus voltage of a second level higher than the first level, at least one dynamic focus electrode supplied with a dynamic focus voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage of a level close to the second level, and at least one anode supplied with an anode voltage of a third level higher than the second level, a first dynamic focus electrode supplied with the dynamic focus voltage is disposed adjacent to the electron beam generating section, and a first focus electrode supplied with the focus voltage is disposed adjacent to the first dynamic focus electrode, when the electron beam is deflected, a first electron lens section created between the electron beam generating section and the first dynamic focus electrode has a focusing function in horizontal and vertical directions, and a first asymmetrical lens section created between the first dynamic focus electrode and the first focus electrode has a relative diverging function in the horizontal direction and a relative focusing function in the vertical direction, and the first electron lens section and the first asymmetrical lens section are electrostatically coupled.
According to a second aspect of the invention, there is provided a cathode-ray tube apparatus comprising: an electron gun assembly having an electron beam generating section which generates an electron beam, and a main electron lens section which focuses the electron beam emitted from the electron beam generating section on a target; and a deflection yoke which produces deflection magnetic fields for horizontally and vertically deflecting the electron beam emitted from the electron gun assembly, wherein the electron gun assembly comprises a plurality of electrodes including a cathode supplied with a voltage of a relatively low first level, which constitute the electron beam generating section, at least one focus electrode supplied with a focus voltage of a second level higher than the first level, at least one dynamic focus electrode supplied with a dynamic focus voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage of a level close to the second level, at least one anode supplied with an anode voltage of a third level higher than the second level, and an insulating support member for supporting and fixing these electrodes, a first dynamic focus electrode supplied with the dynamic focus voltage is disposed adjacent to the electron beam generating section, and a first focus electrode supplied with the focus voltage is disposed adjacent to the first dynamic focus electrode, and the thickness of a peripheral portion of an electron beam passage hole formed in the first dynamic focus electrode for passing the electron beam emitted from the electron beam generating section is smaller than the thickness of the other part of the first dynamic focus electrode.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.